The present invention relates to a disc brake intended particularly for equipping heavy-goods vehicles.
U.S. Pat. No. 4,645,038 describes a disc brake comprising a rotary disc and a caliper mounted on a stationary support so as to straddle the disc and be movable perpendicularly relative to the plane of the latter and carrying two friction elements which are arranged on either side of the disc, the first of these elements bearing on the caliper and the second element bearing, by means of a rigid counterplate, on a threaded pusher, itself screwed in a piece mounted on the caliper so as to be slidable perpendicularly relative to the plane of the disc in relation to the caliper under the action of the drive means, such as a jack, the pusher having a non-circular head which interacts with a retention member of the form matched to this head and which prevents an undesirable rotation of the head and consequently a screwing or unscrewing of the pusher.
According to this document, the head of the pusher is of hexagonal form, and the retention member has the form of a fork with two prongs which come in contact with one or two opposite faces of the head. The rod of the retention member is immobilized by a screw which is mounted in the counterplate of the second friction element and which passes through a hole of the rod of the retention member. When the friction elements have to be changed in order to install others of different thickness, for example because of wear, said screw is removed and the retention member can be used for screwing or unscrewing the pusher in the manner of a box spanner commonly in use.
This arrangement is used in combination with a device for the automatic compensation of wear, the effect of which is to compensate the variations in thickness of the friction elements which are attributable to wear.
This system is on the whole satisfactory. However, it is known that the initial setting of the device for the automatic compensation of wear often requires a high degree of accuracy which is difficult to achieve with a pusher whose head assumes a hexagonal form.
Moreover, it is known that, during braking, the friction elements shift slightly in the direction of rotation of the disc. The retention member, which is fastened at one of its ends to the counterplate fixed to one of the friction elements and at the other end to the pusher, then undergoes very high forces tending to subject it to severe deformation and premature wear.